This application relates to supporting structure for the core and coil assembly of a transformer.
Single phase transformers typically include a pair of windings that are magnetically coupled through a permeable core, or a single coil coupled with two cores. The core and coil assembly is positioned in a tank that is filled with a dielectric fluid. The fluid serves the dual purpose of cooling the assembly and electrically insulating the coils from one another and from the grounded core and tank wall. The insulating fluid also impregnates the Kraft paper utilized as solid insulation within the windings and core and coil assembly. A structure for supporting a core and coil assembly is described in U.S. Pat. No. 4,837,543, which is incorporated by reference.
In accordance with one general aspect of the invention, a transformer includes a tank having a side wall, a core defining a core window, a pair of coils, and a core and coil support member that extends through the core window to support the core and coils. Each coil surrounds a portion of the core and includes a portion passing through the core window.
The core and coil support member includes an upper flange and a lower flange, each flange having a channel formed along an outer surface of the flange that conforms in shape to an inner surface of the core. The core and coil support member also includes a web extending between and connecting the upper and lower flanges. Substantially beyond the flanges, first and second ends are formed from extensions of the web. A support bracket that attaches to the side wall of the tank and supports the core and coil support member, includes three sides that define a channel through which an end of the core and coil member extends.
Embodiments may include one or more of the following features. For example, the core may include first and second vertical portions, the second vertical portion being substantially similar in shape and size to the first vertical portion. The core may include first and second horizontal portions each extending between ends of the first vertical portion and the second vertical portion. The vertical and horizontal portions define the core window.
The core and coil support member may be molded using a reinforced high temperature engineering polymer.
The upper flange may extend perpendicularly from an upper side of the web. Likewise, the lower flange may extend perpendicularly from a lower side of the web. The flanges may be convex in shape. An upper horizontal portion of the core may rest on the upper flange. The coils may rest on the lower flange, and will generally fit between the upper and lower flanges. The coils may also act as a mechanical strut to support the weight of the core on the upper flange.
The channel may include a lowered step. A width of the channel may be substantially equal to a width of a portion of the core facing the core window. The channel may be convex. The channel may serve to lock the core into a stationary position. Moreover, the channel may serve to center the core onto the core and coil support member.
The web may separate and insulate the coils from each other. Furthermore, the web may include a first vertical face that extends perpendicularly from the first end, and a second vertical face that extends perpendicularly from the second end. The vertical face may define an end groove in which the support bracket is secured during assembly and shipping of the transformer. The vertical faces may increase strength of the core and coil support member.
The tank may include dielectric fluid. The web may include a thermal duct design along a side of the web that faces the supported coil. The thermal duct design includes grooves that provide a flow path for the dielectric fluid between the supported coil and the web.
The upper and lower flanges may include a snap-fit connector that permits assembly of brackets for components to the core and coil support member.
In accordance with another general aspect of the invention, a transformer includes a tank having a side wall, a core defining a core window, and a pair of coils. Each of the coils surrounds a portion of the core and includes a portion passing through the core window. The transformer also includes a core and coil support member that extends through the core window to support the core and coils, and a first support bracket that attaches to the side wall of the tank, and supports the core and coil support member. The first support bracket includes two parallel side panels, and a rear panel that connects the parallel side panels to define a channel in a first direction through which the core and coil support member is inserted and positioned. The first support bracket also includes a shelf formed from a lower end of a side panel. The shelf is substantially perpendicular to the first direction. A locking feature is formed from an upper end of a side panel. The locking feature provides a retaining force to the core and coil support member in the first direction.
Embodiments may include one or more of the following features. For example, the first support bracket may include a shelf slot that is formed into a lower end of the side panel across the channel from the side panel that forms the shelf. The shelf slot is made large enough to accommodate and support the perpendicular shelf.
The locking feature may include side apertures through which self-tapping screws are inserted to secure the core and coil support member within the channel of the first support bracket. The locking feature also may include a tab that is bent inwardly after the core and coil support member is inserted into the channel to secure the core and coil support member within the channel of the first support bracket.
The shelf may support at least a portion of the weight of the core and coil support member when inserted into the channel. Alternatively or in addition, the tank or tank bottom may support at least a portion of the weight of the core and coil support member when inserted into the channel.
The core and coil support member may include a first end and a second end that extends from the first end in a direction perpendicular to the first direction. The rear panel may include a spring lever that applies a force to the core and coil support member in the perpendicular direction.
The transformer may further include a second support bracket identical in size and shape to the first support bracket, and attached to an opposite side wall of the tank. The first end of the core and coil support member may be inserted and positioned in the channel of the first support bracket. The second end of the core and coil support member is inserted and positioned in the channel of the second support bracket. The rear spring levers of the support brackets may automatically center the core and coil support member in the perpendicular direction.
The first support bracket may include a projection bent from on a top portion of a parallel side panel in a direction away from the channel. The angle may be based on a size of the coils relative to a size of the tank. Alternatively, the angle may be based on a length of the top portion of the parallel side panel. The projection may also facilitate guidance of the core and coil support member through the channel. Additionally, one or more components may be secured to the projection. The bend angle of the projection may be based on the components secured to the projection.
The core and coil support member serves a number of additional functions. For example, the core and coil support member can be used to anchor and support high voltage leads extending from the coils. The core and coil support member also prevents the corners of the core from cutting a core tube that is inserted into the coil windows. The core tube provides insulation between the core and the coil. The support member also eliminates the need for coil blocks, which had been used to position and clamp the core and coils between upper and lower steel core clamps. This, in turn, eliminates problems associated with the coil blocks compressing the paper at the ends of the coil, which could lead to reduced coil end margins and a higher probability of electrical shorts.
Since the core is in tension in the transformer, that is, there is no compressive stress on the core steel, no-load core losses are reduced. Moreover, elimination of top and bottom steel core clamps and associated metal brackets of prior designs reduces stray losses.
On smaller transformer designs, the core and coil support member can suspend the entire weight of the core and coils. On larger transformer designs, a strut member may be added to each side of the core and coil support member to help support the weight of the core. It is also possible to support the weight of the core by using, for example, a cradle member on the tank bottom.
Tolerances and clearances between the tank wall and the coils can be reduced because the core and coil support member centers the core and coil better in the tank than prior core clamp assemblies. Thus, some transformer designs will accommodate a smaller tank size.
Manufacturing costs are reduced because of the improved manufacturing efficiency. In particular, the core steel is easier to stack because the core and coil support member minimizes the relative movement of the coils with respect to one another. The extra time required to attach the existing steel clamps and insulation pieces is also eliminated. Additionally, the core and coils are easier to install in the tank, and hardware is eliminated by using snap fit connectors. Furthermore, for some implementations, part count proliferation may be reduced from approximately 25 parts to five parts.
The core and coil support member may be clamped in a stacking fixture to keep the coils from shifting during stacking. Furthermore, because the core and coil support member replaces many parts that were previously made of metal, an additional reduction in cost is realized. Finally, because core and coil assembly heights may be reduced in the transformer design, the tank size and amount of dielectric fluid may be reduced, thus further reducing the cost of the transformer.
The design also improves cooling of the coils because there is less obstruction to convective fluid flow around and through the coils. Cooling ducts added to the core and coil support member web further increase cooling efficiency to the coil within the core window. Because the core and coil support member can be made of a high temperature engineering polymer, the core and coil support member can be operated at higher temperatures than current Kraft-based materials without compromising the electrical and mechanical integrity of the design. The engineering polymers also exhibit better long-term aging characteristics than previously used cellulose-based materials. The high temperature engineering polymer provides the structural rigidity necessary to support the core and coils and has high dielectric strength.